Status: Valid
Owner: ----
Labels: Type-Defect Priority-Medium
New issue 3851 by smi...@gmail.com: separable_reduced dsolve solution
incorrect?
http://code.google.com/p/sympy/issues/detail?id=3851
dsolve(eq, hint='separable_reduced')
log(x*f(x)) - log(x*f(x) - 1) == C1 + log(x)
sol=_
checkodesol(eq, sol, f(x))
(False, -f(x)**2*sin(f(x))*cos(x) + sin(x)*cos(f(x)))
solve(logcombine(sol, force=True),f(x))
[exp(C1)/(x*exp(C1) - 1)]
checkodesol(eq,_[0],f(x))
(False, (x*exp(C1) - 1)**2*sin(x)*cos(exp(C1)/(
x*exp(C1) - 1)) - exp(2*C1)*sin(exp(C1)/(x*exp(C1) - 1))*cos(x))
Try to evaluate it at an arbitrary C1 -- in this case C1 = 1
_.subs(C1,1)
(E*x - 1)**2*sin(x)*cos(E/(E*x - 1)) - exp(2)*sin(E/(E*x - 1))*cos(x)
_._random()
6.40813562467874 - 3.544704837125*I
So the expression that is supposed to be zero for all C1 is not, so it
seems to me the solution is wrong (or I am missing something).
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